The present invention relates to a process for producing a methyl methacrylate-based resin article. In particular, the present invention relates to a process for producing an article, which comprises a step of melt processing a methyl methacrylate-based resin with an extruder.
Since methyl methacrylate-based resin is excellent in transparency, it is used as a raw material for optical articles. In processing the methyl methacrylate-based resin into optical articles, beads or pellets of the resin are usually heat melted and molded to the article. This melt processing sometimes causes coloring of the resin, and various researches have been conducted to curb such a coloring.
There are many methods known as the methods for curbing the coloring in the melt processing of methyl methacrylate-based resin, in which a kind or concentration of gas used therein are controlled. For example, Japanese Patent Application Laid-Open (JP-A) No. 63-2004 discloses a method of spinning an acrylate-based polymer under substantially oxygen-free conditions to produce an optical fiber, and JP-A No. 11-19928 and JP-A No. 11-21357 respectively disclose a method of dispersing a specific silicone resin in powders or pellets of methacrylate resin and melting and mixing them while continuously sending dried nitrogen into a hopper of extruder. However, these conventional methods are still insufficient in curbing the coloring of the resin.
One of the objects of the present invention is to provide a process for producing a methyl methacrylate-based resin article which is excellent in curbing the coloring of the resin, to solve the problem described above.
The present inventors have studied on a process for producing a methyl methacrylate-based resin article. As a result, the present inventors have found that the above object can be achieved by conducting the melt-extrusion processing of methyl methacrylate-based resin in a specific gas atmosphere, and have completed the present invention.
That is, the present invention provides a process for producing an article of resin made from at least about 50% by weight of methyl methacrylate, which comprises a step of melt-processing the resin with an extruder, wherein an oxygen concentration of a gaseous phase in a resin feed zone of the extruder falls within a range of from about 0.7% by volume to about 10% by volume.